A branch line coupler is widely used in various kinds of circuits and systems as a basic component, such as a balanced mixer, a balanced amplifier, a power divider, etc.
In some scenarios, for example, in high frequency applications, a size of the branch line coupler is small, and therefore can be integrated onto the surface of a printed circuit board (PCB). Consequently, the branch line coupler can be designed by a single layer PCB or multilayer PCBs.